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Full-swing carrier control for the Browning Mark 3 pt 1 of 2

Discussion in 'CB Radio Modifications' started by nomadradio, Oct 21, 2017.

  1. nomadradio

    nomadradio Analog Retentive

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    Ruh-Roh!
    Turns out this one was over 15000 characters. Had to split it in half.

    Oops.

    Warning! This is a ROUGH DRAFT and not necessarily quite complete.

    To all the folks who asked for this, I'm doing the final tests and getting ready to pack up this toy as a kit.

    With any luck, corrections and revisions to this procedure will follow before I ship a D-I-Y version.

    Installing the Nomad Radio carrier control for the Browning Mark 3 SSB (*not* AM) transmitter.

    HAVE A LOOK AT R51, THE HALF-WATT RESISTOR THAT LOOKS BURNED NEAR THE BOTTOM-CENTER OF THIS PICTURE! If this resistor looks okay, you're probably good to proceed. IF IT LOOKS BURNED, YOU SHOULD FIX THE TRANSMITTER **BEFORE** YOU MODIFY IT!

    [​IMG]

    Installing this control into a broken transmitter will get you a broken transmitter, which is what you have already. And if you contact me to complain, I will simply say "I TOLD YOU SO!"

    If nothing under the chassis looks burned, you should be okay to proceed.

    Connect the mike, dummy load and wattmeter to the transmitter, turn it on and let it warm up. You do NOT need to connect the receiver to do this.

    Now select either USB or LSB, set the meter switch to "MA", key the mike check to see that the bias is set correctly.

    Next select AM mode, key the mike and set the plate tune to its peak setting on the wattmeter. This is the starting point before making any modifications. Removing the bottom cover usually changes the peak setting of the plate-tune control on the rear of the chassis. Doesn't change it much, but you'll find that it peaks at a slightly-different position with the cover in place than it does with the bottom cover removed.

    If the transmitter is not performing properly in its stock condition, DON'T PROCEED ANY FURTHER until it has been repaired. If you install this accessory on a transmitter that is partly crippled or weak, your final result WILL suffer. And I won't be the tiniest bit sympathetic.

    THE MIKE GAIN CONTROL NOW NEEDS TO BE MOVED TO THE FRONT PANEL! Yes, I'm shouting for a reason.

    Before you complain that this won't be necessary, remember that changing the carrier level has the indirect effect of also changing the mike gain at the same time. If you want a variable carrier, you WILL also need access to the mike-gain adjustment from the front panel without removing the cabinet top. Best way is to remove the power switch knob, (1/16-inch hex key) and then the power switch from the front panel. If you plug the transmitter's AC power cord into the socket in the rear of the receiver, you DON'T NEED a power switch for the transmitter on the front panel. The receiver's power switch will now turn them both off at the same time.

    Follow the two black wires (sometimes gray wires) from the power switch to a two-lug tie strip at the back corner of the chassis where the AC-power cord enters the rear panel. Unsolder one of the black wires from the power switch from one lug, and remove enough solder from the lug to leave an opening in the tie-strip lug. Shorten the other black wire to a few inches and strip the end. Now insert the stripped end into the lug where the first black wire was removed and solder. The transmitter's AC power will now be ON whenever the power cord is plugged into a live outlet.



    [​IMG]

    You can usually just move the internal mike-gain control R38 from it's original position to the now-empty hole in the front panel. You'll need three short extension wires from each lug of the mike gain control to reach where it was connected. They will be short enough you should not need to use shielded wire for this. You have plenty of black wire now on hand for that.

    Here's an example that used pink wire.


    [​IMG]

    *** UPDATE! ***
    I'm packing a new 500k audio-taper control with the installation parts. The old internal mike-gain control is 40 years old or more, and could have a defect, or be tricky to remove and reconnect. Including a new mike-gain control eliminates one potential source of trouble.

    The final part of preliminary setup is to replace C47, the skinny 1-inch diameter two-section "can" filter capacitor. No need to take it loose from the chassis. The two 10uf 450-Volt radial capacitors included with the install kit will each take the place of one section of C47.

    One of the two lugs under C47 has a single red wire on it. Clip this wire from C47 and follow it to the other end. The other end of this red wire is on the inboard-end lug of a tie strip just towards the front from the main 3-section filter capacitor. Remove the red wire from this lug. One of the 10uf 450V radial caps gets the positive lead into this lug. The negative lead goes to the ground lug next to the lug on the inboard end. The inboard-most lug of this strip, where we removed the red wire and put the new cap's positive lead also has a 1/2-Watt resistor attached to it. Should have the color bands orange-orange-red, indicating a resistance value if 3.3k.

    [​IMG]

    If it appears burned like the one in the picture, STOP RIGHT NOW BECAUSE YOUR MODE SELECTOR IS BREAKING DOWN!

    Besides, when R51 burns up like this you won't have mike audio any more. Or at least you shouldn't. Installing the carrier control into a transmitter with a burned mode selector is just a bad idea. We won't cover the ways to work around this problem right now. Maybe another time.

    For now, you need to track down a transmitter that doesn't burn up R51, so you'll have a functioning transmitter to use for the rest of this procedure. Hmmm. Maybe I should point out the need to inspect R51 BEFORE you install the two caps and move the mike-gain control, maybe?

    [​IMG]

    The other lug of C47 has a red wire and a either 10k or 33k 1-Watt resistor R43 attached to it. Clip both of these as close to the lug as you can. Strip the end of the red wire and slide the supplied black sleeve over it. Tin the end of R43 and the stripped end of the red wire. Lap-solder them together and slide the sleeve over the splice.

    [​IMG]

    Follow the red wire to pin 1 of V8, the 12AU7 tube. Suck enough solder from the pin 1 lug of the socket to insert the positive lead of the other 10uf 450V radial cap. Solder the cap's negative lead to the nearest ground lug on the tube socket's mount saddle.

    [​IMG]

    This completes the preliminary setup before taking stuff loose, drilling holes and such.

    Now, hook up the transmitter and TRY it to see that it still functions normally. Make sure the new front-panel mike-gain control functions smoothly. If it's scratchy when you turn it, this calls for a shot of control cleaner. Don't skip this step, it's important. If it won't work correctly now, STOP and find out why before altering anything else! Installing the carrier control into a broken transmitter just muddies the water and might make it more work to track down and fix what's broken.

    Once you're SURE the transmitter still works, unplug everything from it. If your transmitter still has the original-type 110-Volt DC type relay, you can drain the transmitter's filter caps by holding the mike keyed for 30 or more seconds after you have pulled the plug.


    Next item to get altered is the 10-Watt resistor R49. The resistance value is originally 2k, but will often be modified or even jumped out with a wire across it. The factory schematic says it's a 4-Watt part, but every one I have seen has a 10-Watt part from the factory. This is the resistor that determines the carrier power in AM mode. The inboard end of the tie strip where it's mounted is the 320-Volt transmit-only B+. This tie point also has one end of R48 attached to it, the 1.5k 1/2W resistor feeding into pin 9 of V9, the 6BQ5 modulator tube. Remove enough solder from this lug to accept one more resistor lead.

    [​IMG]

    The other (outboard) end of R49 gets unsoldered and pulled out of the lug. We will call this one the "output" lug. Remove enough solder from the output lug after R49 is pulled out of it so a wire and a capacitor lead can be connected here later. With any luck the now-loose lead of R49 will reach the lug next to the one you pulled it out of.

    The early (non-ALC) version of the transmitter has a brown wire (only) here. Remove and sleeve over the loose end before inserting the now-loose output end of R49.


    THIS LUG IS ALREADY EMPTY ON SOME PRODUCTION RUNS. If so, tuck R49's loose lead into this lug.

    IF A WIRE AND RESISTOR ARE SOLDERED HERE, unsolder them. Slide a length of sleeve over the end of the wire and lap solder the loose ends to each other. No need to twist them, the solder alone will be secure. Just hold the two ends parallel and solder. The sleeve keeps the exposed lap joint from getting into trouble. Clear the solder from the lug to insert the free end of R49.

    If R49 is damaged, missing or just dead wrong, you can replace it with the 2k 10-Watt resistor that's included. Just be sure to leave a hole cleared in the 320-Volt lug.

    Now that R49 is tucked into the lug next-inboard from the one where you found it, the 1uf 450V capacitor gets the positive lead into this lug. The negative lead goes into the lug where you removed one end of R49. Don't solder anything yet. As a rule, only the negative side of this cap is marked with a "-". The positive lead is also longer than the negative lead.

    [​IMG]

    The lug on this same tie strip next-inboard to the one where we moved R49 must also be cleared if it has parts soldered to it. Same routine as above. Pull them loose from the lug and remove the solder from the lug's eye. If there is ONLY ONE wire here, just slide a piece of sleeve over the end of the wire and tuck it away where it won't get into trouble.

    Early non-ALC version has a 10k 10W and a red wire leading to the Spot button. Use the next-inboard lug, Has only a gray wire on it. Remove, sleeve the end.

    The green 15k resistor gets one end into the 320-Volt end lug of this tie strip. The other end goes into the second lug we just cleared.

    [​IMG]

    Go ahead and solder the 320-Volt lug at the inboard end of the tie strip now, but not anything else, yet.
     
    Shadetree Mechanic likes this.

  2. nomadradio

    nomadradio Analog Retentive

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    Part 2 of 2

    The small circuit board that serves as the pickup for the transmitter's SWR meter is held under the chassis by a sheet-metal screw with a 1/4-in hex head. Remove this screw.

    [​IMG]

    The control transistor will be mounted to the topside of the chassis at this hole. The #4-40 machine screw on the heat sink's mounting pillar goes where the sheet-metal screw on the underside was removed. Put the tooth washer over the screw. It will discourage the metal pillar from spinning once the screw is tight.

    [​IMG]

    The wires on the transistor board go into the three vent holes in the deck just to the front of the control transistor.

    [​IMG]

    R50, the 10k 10 Watt resistor has been moved aside for improved visual clarity. You should not need to disturb this part.

    The brown wire now gets hooked to the tie-strip lug where we moved one end of R49. The positive lead of the 1uf capacitor is also on this lug. Go ahead and solder this one now. Nothing else gets hooked to this lug.

    The yellow wire has been stripped a couple of inches down from where it's attached to the control-transistor board. Pass it through the lug where we removed one end of R49, where the negative side of the 1uf 450V radial capacitor is. Solder this one now.

    [​IMG]

    The blue wire also has a stripped spot. Pass it through the lug at the outboard end of the green 15k 7-Watt resistor. Solder it now.

    [​IMG]

    The remaining 11 inches of both the yellow and blue wires are now inserted into the vent hole near the power tansformer as shown.

    [​IMG]

    The control board has three wires already installed on it. The gray wire is power, and goes to the transmitter's 6.3VAC heater supply. The single white wire is the feedback input from the modulation transformer's secondary, and has a 47k 2 Watt resistor soldered to the far end. The fat shielded 2-conductor wire will be soldered to the front-panel carrier control.

    [​IMG]

    [​IMG]

    The control board requires two 5/32-in. holes spaced 1-3/4 in. apart and half-inch or more in from the rear edge of the chassis. Position the board far enough from the power transformer that your drill chuck won't rub against the transformer while drilling. Move it too far from the transformer, and you'll end up drilling the inboard-end hole through the receiver coax under the deck. Position it and mark the holes through the bracket holes.

    [​IMG]

    A center punch will improve the accuracy of the screw holes for the control board.

    [​IMG]


    The gray wire and the white wire with the resistor on it also go below deck. The shielded cable for the front-panel control should get pushed through a hole below deck before trying to bolt down the control board. It's way too stiff to stuff into the hole after the control board is attached.
    The end of the yellow wire goes into the hole at the top corner of the board marked "E". The end of the blue wire into the hole marked "B".

    [​IMG]

    It's a bit tricky to push the screws up from below deck and get a nut onto it when passed through the bracket hole, but they'll fit and tighten up just fine.


    [​IMG]

    Route the shielded control cable under the chassis to the front panel near the SWR Cal knob.

    Clip the wires that lead to the SWR Cal control. Remove the knob and the old control. Save the toothed lockwasher.

    [​IMG]

    Mount the new carrier control in the hole. The bushing is smaller than the original, but putting the tooth washer between the control and the panel will serve to hold it centered. The flat washer should cover the original hole on the front panel so the nut won't interfere with the edge of the hole.

    [​IMG]

    One lug has been clipped off the new carrier control. The red and black conductors on the end of the white shielded wire solder to the two lugs on the control. Doesn't matter which wire goes onto which of the two lugs.

    [​IMG]

    Yes, I know the above pic is NOT from a Mark 3. I screwed up the Mark 3 pic for this, but this one gets the idea across.


    The gray wire from the control board goes to pin 4 of V2, the 6BA6 tube. This is where the 6.3-Volt AC wire from the transformer feeds into V2 and into a bunch of black wires leading to all the other tubes. Simply lap-soldering the end of the green wire here will work, so long as your iron is hot enough to heat the whole bundle of wires at this lug.

    [​IMG]

    The white wire with the 47k resistor on the end gets routed to the inboard end of R23, a 15k 2W carbon-comp resistor. It's on a tie strip under the deck just towards the front from the relay socket. Solder the end of the 47k resistor to the end of R23 closest to the final. A green wire that goes back to the modulation transformer is also soldered to this lug.


    [​IMG]

    Yeah, I know the resistor hasn't been soldered yet in this pic. Just too burned out on this project to go back and shoot it again just to show that you need to solder it.

    Now that everything is connected, double-check every connection that was disturbed to see that all of them have been securely soldered back down.

    Connect the dummy load, wattmeter, mike and power up the transmitter. Give it a minute or so to warm up.

    Turn the carrier knob (SWR Cal) full to the right (clockwise). Key the mike and set the upper orange trimpot (marked "Set Max") on the control board for just a bit less than the max power you see on the wattmeter. If your transmitter shows much more than 4 Watts max carrier, feel free to set this trimmer to a max carrier power of 4 Watts.

    Next, turn the carrier knob on the front panel full to the left (counterclockwise) and set the lower of the two orange trimpots marked "Set Min" so that the carrier power just bumps up about a quarter of a Watt above it's minimum. This is to eliminate dead spots at either end of the knob's range.

    Finally, now set the front-panel carrier control to it's minimum end and set the black trimpot on the corner of the control board (marked "SetThre" so that the carrier power just barely increases above where it was set in the previous steps. If you set it too high, your modulation level will be compromised. If you set it too low, you won't get any swing at low carrier levels.

    When the black trimpot is set correctly, you will usually see between 3/4 and 1 Watt minimum carrier power. The peak modulated power should be essentially the same at any carrier-level setting

    Gotta get the two D201 versions edited to post.

    Real Soon Now.
    We always say that.

    73
     
    #2 nomadradio, Oct 21, 2017
    Last edited: Oct 21, 2017
    Shadetree Mechanic and wavrider like this.
  3. Riverman71

    Riverman71 Part-time Member

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    Outstanding! (y)(y)(y)
    Now all I need is a soldering iron, a Mark III, and an inkling of what you just said. :ROFLMAO:

    If I had it to do all over again, I'd try and persuade my mom to invest in radio electronics training for me rather than piano lessons. :)
     
    Shadetree Mechanic likes this.
  4. 711

    711 Active Member

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    Nomad,
    Do you have a list of kits you sell including this one?
     
    Shadetree Mechanic likes this.

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